This invention relates to a sensor for an engine control and more particularly to an improved sensor and CDI arrangement for firing the spark plugs of an internal combustion engine.
In connection with spark-ignited internal combustion engines, it is a common practice to utilize a CDI ignition system for firing the spark plugs. This type of system employs an electrical circuit in which a capacitor is charged by a charging coil. A solid state device then is controlled by a further signal from the engine so as to provide a timing indication and this signal is utilized to ground the capacitor and induce a voltage in the primary winding of a spark coil for firing the spark plug. This type of system is quite effective and permits adjustments in the time curve to be made without utilizing mechanical devices as was formerly required.
FIG. 1 illustrates a conventional type of CDI spark ignition system and will be described in detail so as to point up several disadvantages of the conventional-type system normally utilized. As seen in the upper view of this figure, the ignition system is indicated schematically and it includes a terminal 11 that is connected to a spark plug. The terminal 11 is in circuit with the secondary winding of a voltage step-up spark coil 12.
A voltage is induced through this spark coil by a CDI ignition system identified generally by the reference numeral 13 and shown in full detail in the middle view of this figure. The CDI system operates in the manner previously described so as to discharge a capacitor to induce a current voltage in the primary winding of the spark coil 12 so as to fire the spark plug through the terminal 11. The CDI unit 13 cooperates with a flywheel-driven device, indicated generally by the reference numeral 14, and which includes the flywheel 15 on which a plurality of permanent magnets 16 are mounted. These magnets 16 cooperate with a fixed charging coil 17 and a pulser or trigger coil 18, both of which output their signals to the CDI unit 13.
Referring now specifically to the middle view of this figure, it will be seen that the charging coil 17 charges a capacitor 19 through a diode 21. A solid state switching device, such as an SCR 22, is provided in a circuit to the ground through a further diode 23. This circuit is also in parallel with the primary winding 24 of the step-up spark coil 12. The secondary winding 25 is in circuit with the gap of the spark plug associated with the terminal 12, which spark plug is indicted schematically at 26 in this figure.
Finally, the pulser or trigger coil 18 is in circuit with a switching circuit 27 that switches the SCR 22 so as to permit the capacitor 19 to discharge to the ground through the diode 23 and induce a voltage in the primary winding 24 for firing the spark plug.
As may be seen from the lower portion of FIG. 1, the charging coil generates a sinusoidal wave, the positive segments of which are utilized to charge the capacitor 19 through the diode 21. The capacitor charge is shown in the middle range curve of this view and it will be seen that the capacitor reaches its maximum charge at about the time when the charging coil output reaches its maximum and this charge is then held due to the presence of the diode 21 in the charging circuit.
This charge is maintained until the pulser coil 18, through cooperation with the switching circuit 27, outputs the signal to switch the SCR 22 to a conductive state so that the capacitor 19 can discharge and fire the spark plug. Thus, the charge on the capacitor is held for a time t.sub.i.
This system, although extremely effective, does have some areas where it could be improved upon. The first of these is that it requires two separate sensing devices in the form of separate windings and two separate magnets. This not only adds to the cost of the system, but also somewhat dictates the time at which the spark plugs can be fired due to the requisite spacing of the magnets 16 and the associated coils 17 and 18. In addition, this type of system does require the utilization of the diode 21 so as to permit the capacitor to hold its charge and not discharge through the charging coil 17.
It is, therefore, an object of this invention to provide an improved and simplified CDI ignition system.
It is a further object of this invention to provide an improved CDI ignition circuit that permits the use of a simplified and single sensor for both charging the capacitor and triggering its discharge.
It is a still further object of this invention to provide an improved CDI ignition system that permits a wider latitude in the timing of firing of the spark plugs.